Field of the Invention
The invention relates to an aqueous solution consisting of an organic or inorganic base, hydrogen peroxide and a complexing agent for cleaning a semiconductor substrate.
The process for the production of integrated circuits incorporates multiple cleaning steps for removing surface contamination. Contamination on the wafer surface can in the simplest case be removed by blowing-off with purified nitrogen. In most cases, however, this does not remove all the particles. Another possibility is rinsing with filtered deionized water (containing a wetting agent) or with suitable cleaning chemicals, such as acetone or isopropanol. This type of cleaning is either carried out in a tank under the action of ultrasound (MHz frequencies), or the liquid is sprayed at high speed onto the wafer surface from jets (jet scrubber). Mechanical brushing in a scrubber is also used, principally after CVD deposition. The particles that are brushed off are rinsed off the wafer surface using deionized water or a solvent.
In the production of integrated circuits, a number of chemical wafer cleaning steps is generally necessary. They are generally carried out after removal (stripping) of a resist mask and wherever possible immediately before a coating is applied. The semiconductor wafers are either dipped into suitable chemical baths, frequently under the action of ultrasound, or the cleaning liquid is sprayed onto the wafers in a cleaner.
A frequently used process is RCA cleaning (RCA Review, page 18-206, June 1970), which consists of two separate cleaning steps:
In the first cleaning step, RCA-1 or SC-1 (Standard Clean 1), the wafer to be cleaned is immersed in an alkaline cleaning solution consisting of one part of ammonia, one part of hydrogen peroxide and five parts of water, at a temperature of about 70.degree. C. and then rinsed with ultrapure water in order to remove particles and organic contamination from the wafer surface. PA1 This is followed by the second cleaning step, RCA-2 or SC-2 (Standard Clean 2). In this step, the wafer to be cleaned is dipped into an acidic cleaning solution consisting of one part of HCl, one part of hydrogen peroxide and six parts of water, at a temperature of about 70.degree. C. This is again followed by rinsing with ultrapure water in order to remove the metal contamination originating, inter alia, from the SC-1. PA1 1) the solubility of the cryptand and/or PA1 2) the adduction of the cryptand onto the semiconductor substrate and/or PA1 3) the metal complexability and/or PA1 4) the stability of the cryptand to oxidants, and m, n and o are 2 or 3, and p is 1 or 2.
In general, the wafer surfaces after the SC-1 treatment are contaminated by Fe, Al, Ca, Mg, Zn and/or Cu ions and/or other metallic ions. The metal contamination originates from the process steps carried out immediately before the cleaning step. Contamination arises through contact with stainless steel, leaching of metals from fittings and piping material and diverse types of metal contamination from individual processes in semiconductor manufacture, such as dry etching, ion implantation and coating with photoresists, etc.
After the SC-1 treatment, the surface of the wafer is usually contaminated by approximately 10.sup.11 to 10.sup.12 iron atoms per cm.sup.2, approximately 10.sup.11 to 10.sup.13 aluminum atoms per cm.sup.2, and approximately 10.sup.10 to 10.sup.11 copper and zinc atoms per cm.sup.2.
In order to counter this problem, diverse complexing agents are nowadays added to the cleaning solutions. For example, Non-Prosecuted German Patent Application DE 38 22 350 A discloses a process in which ethylenediamine tetraacetate (EDTA) is proposed as the complexing agent. However, the use of EDTA has proven relatively ineffective.
Furthermore, European Patent Application EP 0 276 774 A discloses a cleaning solution in which pentavalent phosphorus compounds are proposed as the complexing agent. This proposed solution has also proven to be relatively ineffective in practice.
Finally, European Patent Application EP 0 496 605 A discloses a process for cleaning semiconductor substrate surfaces in which compounds containing phosphonic acid groups or salts thereof are proposed as the complexing agent. The phosphonic acid compounds prove to be very effective in practice against contamination by iron ions, which generally cause relatively severe problems. On the other hand, however, the phosphonic acid compounds proposed in European Patent Application EP 0 496 605 A do not have a complexing action vis-a-vis copper and zinc contamination.
Furthermore, all known wet-chemical wafer cleaning processes have the common feature that they must be carried out at a temperature of 70.degree. C., which results in increased costs and equipment complexity. Furthermore, all known wet-chemical cleaning processes include two cleaning steps, as originating from the above-mentioned RCA cleaning.